Automatic watering systems for batteries employ independent valves in each cell of the battery to control the flow of water into the cells for replenishing the aqueous electrolyte that is lost during battery charging. Such batteries typically comprise a casing containing a number of individual cells, each holding an electrolyte solution in which plates are immersed. Examples of batteries having an aqueous electrolyte include nickel-cadmium batteries or lead-acid type batteries. Oxygen and hydrogen gases are produced during charging as a result of electrolysis of the water. The electrolysis causes a loss of water from the electrolyte solution, and, as a result, such batteries require periodic replenishment of the lost water.
It is advantageous for the valves to operate effectively across a wide range of water pressures. They should be sensitive enough to operate at low pressures of about 4 psi, but stable enough to operate at high pressures of about 50 psi.
Valves currently in use for battery watering may be classified in one of two categories, i.e., hydrostatic or hydrodynamic. Hydrostatic valves typically rely on a float buoyed by the electrolyte to open and close the valve, while hydrodynamic valves rely on a venturi-based mechanism for actuation. Both types of valves can employ a positive stop configuration. Positive stop valves have a closing member, typically a piston, that moves within a pressurized chamber through which the water or other fluid flows. Upon actuation by the float or venturi mechanism, the piston engages with or disengages from a seat within the chamber to close and open the valve. In the positive stop configuration, the piston moves into the closed position with the water flow or pressure. Positive stop valves, be they hydrostatic or hydrodynamic, suffer from the same disadvantage, in that hydrodynamic drag on the piston engendered as water flows through the valve can cause the piston to close the valve prematurely in response to the water flow or pressure, and not in response to the fluid level as intended. Positive stop valves in particular, tend to close prematurely when operated at high pressures which generate high drag forces on the piston and its actuating mechanism. This characteristic limits the range over which positive stop valves may be effectively employed to the lower pressures. There is clearly a need for a valve that can operate over a large pressure range, encompassing both high and low pressures and flow rates, without premature closing due to high hydrodynamic drag.